class_docstr: Proportional Prioritized Experience Replay.
      
class_docstr_tok: ["Proportional","Prioritized","Experience","Replay","."]
code: def store(self, item, delta=None):
      assert len(item) == 5  # (s, a, r, s', terminal)
      if not delta:
          delta = self._max_priority
      assert delta >= 0
      ps = np.power(delta + self.eps, self.alpha)
      self.elements.add(item, ps)
  
file_path: PARL/benchmark/fluid/Prioritized_DQN/proportional_per.py
imports: import numpy
label_desc: Use image node_id 3 for calling the ProportionalPER obj's underlying member method code with example usage: obj.store(item, delta) without return types